The present invention relates generally to liquid crystal electro-optic apparatus, and more particularly to such an apparatus for controlling the stable state of molecular orientation in accordance with the application state of an electric field to a ferroelectric liquid crystal. The present invention may be employed, for example, in optical shutters and wall-mounted televisions.
As electro-optic apparatus using a liquid crystal are known so-called DSM type, TN type, G-H type and STN type electro-optic apparatus using the electric field alignment effect of a nematic liquid crystal phase which apparatus are being put into practice. In such apparatus, the average direction of the long axes of the liquid crystal molecules assumes a preferable orientation in applied electric fields due to the permittivity aerotropic characteristic of the liquid crystal. Here, since the coupling between the applied electric field and the permittivity aerotropic characteristic is considerably weak, the electro-optical response time is extremely long, for example, several milliseconds to several tens milliseconds. In addition, variation of the transmission factor with respect to the applied voltage does not have sufficient non-linearity. Thus, limitations are given for applications owing to the aforementioned disadvantages. Accordingly, various types of liquid crystals have been developed with a view to eliminating the aforementioned problems. One known approach is a ferroelectric liquid crystal which has been developed by Meyer and other persons and announced in Le Journal de Physique, 36 Vol. 1975, L-69. As a result of research made by some research groups, the liquid crystal has been known to have three electro-optical effects. Of these effects, two relate to response from several microseconds to several tens microseconds which is in turn useful for producing high-speed liquid crystal electro-optic apparatus as illustrated in Japanese patent provisional Publication No. 56-107216 and Japanese Patent Provisional Publication No. 60-195521, for example, where the torsion structure of the ferroelectric liquid crystal is released due to forces of wall surfaces so that the relation between orientation states of liquid crystal molecules, becoming parallel to the wall surfaces, is varied in accordance with the polarity of an applied voltage and a transient molecular scattering state occurring at the time of inversion of the polarity of an electric field applied to the ferroelectric liquid crystal is utilized. On the other hand, the remaining electro-optical effect relates to a third stable state which is present in first and second stable states of liquid crystal molecules and at the time of a field-free state occurring in accordance with the direction of an applied electric field as briefly disclosed in a paper (titled "&lt;"-SHAPED LAYER STRUCTURE AND ELECTRO-OPTIC PROPERTIES IN SURFACE STABILIZED FERROELECTRIC LIQUID CRYSTAL CELLS") in proceedings of the first ferroelectric liquid crystal international symposium. Although advantages of the aforementioned third electro-optical effect may be useful for improvement of the liquid crystal electro-optic apparatus, no technique effectively applying the third electro-optical effect has appeared heretofore.